Tuesday, February 4, 2014

Lavoisier crater

LROC NAC mosaic of the the fascinating floor of Lavoisier crater. A concentric crater is seen in the lower left corner of the image, and fractures trending northwest to southeast. 10 km field of view from LROC Narrow Angle Camera (NAC) mosaic M1114711232, LRO orbit 16511, February 5, 2013; 49.9° incidence angle, resolution 1.4 meters per pixel from 141.96 km [NASA/GSFC/Arizona State University].

Raquel NunoLROC News System
Many intricately fractured crater floors are found in the northwestern portion of Oceanus Procellarum, near the boundary between mare and highlands.

Today we peer into one of these, Lavoisier (70 km, 38.17°N, 81.25°W). Most floor-fractured craters (FFCs) occur in or near ancient basins; some of the basins were flooded with mare basalt. We see three fractures in the image above: one running diagonally trending northwest to southeast, the second running almost parallel and through the rim of a concentric crater, and the third at lower right perpendicular to the first.

These fractures not only cut across the floor center, but they are also found skirting the walls of the crater on the floor. One proposed formation mechanism is post-impact modification by volcanic related activity, such as magmatic intrusion. The other proposed mechanism is viscous relaxation.

HDTV sequence, north over the western edge of Oceanus Procellarum and Lavoisier crater

View south over the fractured floor of Lavoisier, from the Terrain Camera (TC) of Japan's lunar orbiter Kaguya (2007) [JAXA/SELENE].

Much like floor fractured craters, concentric craters are often found near mare/highlands boundaries. Today's Featured Image includes an example of a concentric crater. Concentric craters contain an inner rounded rim whose formation mechanism is not entirely understood, see the WAC context image below. One theory is that concentric craters are the surface expression of a subsurface discontinuity, such as a layer with different mechanical properties. However, as we look in our Featured Image adjacent to the concentric crater, we see a similarly sized (~6 km) crater that does not exhibit concentricity! If the concentric crater was formed by an impactor hitting a layered target, it would mean that the layering was extremely localized, otherwise the adjacent crater would also be concentric. Another proposed formation mechanism is uplift from magmatic intrusions.

LROC low Sun (high incidence angle) LROC Wide Angle Camera (WAC) mosaic of a 250 km-wide portion of the west-northwestern edge of Oceanus Procellarum. The area visible in the LROC Featured Image released February 4, 2014 is roughly outlined in red [NASA/GSFC/Arizona State University].

So we don't have the whole story yet, but scientists are hard at work trying to understand these processes. Geologists are studying the morphologies and compositions of lunar features, theorists/dynamicists are computationally simulating the cratering process, and experimentalists try to replicate these craters in the laboratory with high energy events. One day, on-site investigations of the lunar subsurface will also assist in determining the origin of the myriad of features seen across the lunar landscape.

If you were to go to Lavoisier crater, which structures would you like to study? Pick them out by surveying the full resolution NAC mosaic, HERE.